A typical fuel system for use with an internal combustion engine may include a liquid pump, a tank, a filter, a regulating valve, and fuel injectors, and a series of conduits that interconnect these components. The tank is located downstream from the liquid pump, whereas the filter, the regulating valve, and injectors are located upstream. The liquid pump has an inlet and an outlet and draws fuel from the tank into its inlet and discharges fuel from its outlet to the other components of the system.
Air or vapor can enter these fuel systems, causing the liquid pump to dry out and lose pressure. This pressure loss may render the pump unable to overcome restriction created by the resistance of the filter, the regulating valve, and the injectors. Thus, the pump becomes unable to pump fuel to the injectors. This may cause the engine to stall, operate inefficiently, or fail to start. When this occurs, the fuel system must be primed. Priming purges/bleeds air from the system, thereby rewetting the pump so that it can pump fuel through the filter and to the injectors.
Some known systems include hand pumps for pushing air out of the system and thereby priming the engine. Although these pumps can be effective, an operator does not always have the time or the strength to pump the number of strokes necessary for properly priming the engine. Additionally, it is often difficult to generate enough pressure with these pumps to open the regulator valve, which may be necessary for pushing air to the tank.
Other known systems include a bypass passage around the pressure regulating valve and/or the cylinder head. This bypass passage includes a restriction orifice that allows air to pass without restriction, but is relatively restrictive to liquid flow. Such a system is shown in portions of U.S. Pat. No. 6,701,900 to Millar et. al. entitled “Quick Priming Fuel System and Common Passageway Housing for Same.” These systems, however, have shortcomings. For example, restriction orifices do not work well in fuel systems where the cylinder head is elevated above the rest of the fuel system. This is because most air introduced in the system rises past the restriction orifice, without entering the orifice, and this air continues rising until it reaches the cylinder head. Eventually, this risen air must pass through the cylinder head. The restriction orifice can also disadvantageously compete with the regulating valve. Because the restriction orifice is always open, it affects the fuel pressure when the regulating valve opens for regulating the fuel pressure. The restriction orifice can also allow fuel to drain back to tank when the engine is turned off. If there exists an opening to atmosphere at any point in the system, e.g., a tiny hole in a hose, the system will suck in air through that opening for filling the volume vacated by the drained fuel.
Another known system for priming is to utilize a manual valve in a bypass passage around a pressure regulator and/or the cylinder head. The manual valve is typically opened when the engine is off and is being primed via a hand priming pump. The manual valve is open to allow air to bleed out of the fuel system, and the system is primed when fuel is expelled from the valve. Upon noticing the appearance of fuel, the operator then closes the manual valve and cranks the engine to start in a conventional manner.
Other systems for priming utilize an open-close valve in a bypass passage around a pressure regulator and/or the cylinder head. This type of valve is open when the fuel pressure is between zero and a low pressure, e.g., the valve is open between 0 and 30 psi, for bleeding air to tank and thereby facilitating priming. The valve closes and remains closed once the fuel pressure rises above the low pressure threshold, e.g., the valve is closed when the fuel pressure is above 5 psi. This system of using an open-close valve is disadvantageous because the valve is open when the engine is off. This allows fuel to drain back to tank, possibly causing the system to suck in air.
The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the present disclosure nor to limit or expand the prior art discussed. Thus, the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use within the present disclosure, nor is it intended to indicate that any element is essential in implementing the present disclosure.